The Devil’s Language?

While looking up Japanese idioms for a section of my newest story draft, I found this interesying little tidbit on a site on the language:

In the 16th century, St. Francis Xavier reported to Rome that the Japanese language had been devised by the Devil to prevent the spread of Christianity in Japan. Many who have attempted to crack the Japanese market and learn Japanese might agree with St. Francis!

Occasionally I joke with Koreans that the Korean language was designed by the Japanese to make transmission of Western technical knowledge into Korea slower, as a part of their colonial invasion, and that Old Korean was much easier to learn.

It’s not true, they insist, not getting the joke. Whereas Quebecois occasionally find my theory about poutine being designed by the English to immobilize the French-Canadians a little more penetrable.

Anyone know how to say “What the hell is this [S.O.B. talking about]?” or something like that in Japanese, by the way? I’m looking for something vaguely rude, even verging on cussing, with that meaning. Something that would be said by a male native Japanese speaker just at the beginning of a violent confrontation. I’m assuming “Nani?” just wouldn’t cut it at that point. Or would it?